The present invention relates generally to antenna systems in a cellular network and more particularly to a method for facilitating an adjustment of the gain of an antenna system in a radio base station during the base station's installation process.
The majority of countries have mobile radio systems. In order to enable the system's operators to satisfy capacity expectations with the frequency bands allotted to the operator, the mobile radio system is divided into geographical areas that are called cells. The cells contain radio base stations which allow mobile terminals to communicate with other mobile terminals and with a land-based telephone network. One radio base station can cover several areas within the cell more efficiently with the aid of directional antennas. In such a case, these areas are typically called sectors.
Radio channels that are allotted to the mobile radio system are shared by those cells that are included in the system. The same set of radio channels can be used in several cells. Cells that use the same radio channels can be spaced sufficiently apart so as not to interfere with one another. This demands careful cell planning.
First-time planning of a cell involves, among other things, choosing the respective positions of radio base stations and antennas. The power at which the antennas are permitted to transmit is governed by the positions of the radio base stations and the antennas, which in turn governs the area covered by the base stations. Improvements in capacity, for instance, may make smaller cell sizes desirable and, therefore require a reduction in the maximum permitted output power.
In order to plan a cell accurately and, at the same time, provide the highest possible output power without exceeding a permitted power level, it is desirable to control the antenna's gain both accurately and quickly.
FIG. 1 illustrates a typical base station with an associated active antenna system which, as described above, is capable of transmitting and receiving signals. Base station 100 includes a power amplifier 102, a low noise amplifier (LNA) 103, a duplex filter 104 which operate in a well known manner. Base station 100 also includes a ground-based processor 106 the operation of which will be described in more detail below. The base station 100 is connected to the antenna system 140 via feeding cable 120. The feeding cable is a coaxial or other similar type of cable. The antenna system includes an attenuator 142, a power amplifier 144, a circulator 143, a low noise amplifier 149, an antenna-mounted processor 146 and a sensing element 148.
As illustrated in FIG. 1, base station 100 is also attached to a telephone network 160. One skilled in the art will appreciate that the telephone network 160 could be either a Public Land Mobile Network (PLMN) or a Public Switched Telephone Network (PSTN).
During typical base station operations, the output power of the antenna system 140 requires adjustment in order to optimize system performance and prevent an overdrive of the antenna's power amplifier 144. Such an adjustment is desirable in order to compensate for temperature variations or loss attributable to the feeding cable which affects the system's output power. It may also be desirable to adjust the antenna's output power in order to increase/decrease the size of the antenna's coverage area.
According to conventional techniques, the output power of the antenna is measured, via sensing element 148. The measured value is transferred to the antenna-mounted processor 146 where it is compared to a reference value which is supplied from the ground-based processor 106 in the base station 100 via a communications line 122. The reference value is provided to the ground-based processor from telephone network 160. The reference value is set according to calculations from the base station controller (BSC) or the mobile services switching center (MSC) (not shown).
Once set, the reference value is continuously compared to the antenna's measured output power. When the measured output power is determined to be above or below the reference value, the attenuator 142 is set to the appropriate attenuation value in order to adjust the antenna's gain. By adjusting the gain, the desired output power of the antenna is achieved.
During those situations where it is desirable to change the reference value, e.g., when the antenna's coverage area is to be increased/decreased, conventional techniques require reprogramming of the software and/or adjusting the hardware in the telephone network and the base station. This conventional technique may not only be time consuming, but also expensive.
Therefore, there exists a need for a method which quickly and accurately measures and adjusts the gain of an antenna system.